Inspection method and inspection apparatus for inspecting electrical characteristics of inspection object

ABSTRACT

At least one pair of electrode formed on a mounting surface of a stage is in contact with a conductive layer formed on a first surface of an inspection object, and an electrical path is formed between the both by using a fritting phenomenon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of PCT Application No.PCT/JP2004/008300, filed Jun. 8, 2004, which was published under PCTArticle 21(2) in Japanese.

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2003-164349, filed Jun. 9, 2003,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inspection method and inspectionapparatus for inspecting the electrical characteristics of an inspectionobject. More specifically, the invention relates to an inspection methodand inspection apparatus capable of inspecting the electricalcharacteristics of an inspection object such as a device (for example, apower transistor) or each inspection object of plural devices formed ona single substrate.

2. Description of the Related Art

Upon inspecting the electrical characteristics of a device such as apower transistor, a large current and voltage are applied. For thepurpose, it is necessary to bring probes into contact with electrodes ofthe device securely. In case of a device such as a power transistor, astage, on which an inspection object is to be mounted, is electricallyconnected with an electrode (for example, a collector electrode) formedon the rear face of the inspection object. When, in this state, theelectrical characteristics of the inspection object are inspected, thesurface of the stage needs to be brought into secure contact with thecollector electrode formed on the rear face of the inspection object.

Patent document 1 and patent document 2 disclose a technology forbringing the surface of a stage into electrical contact with a collectorelectrode formed on the rear face of an inspection object.

According to the technology described in patent document 1 (Jpn. Pat.Appln. KOKAI Publication No. 63-258036) (claim and page 2, upper rightcolumn, line 2 to lower left column, line 7), voltage applyingelectrodes for applying a voltage to a semiconductor wafer and voltagemeasuring electrodes for measuring a voltage of the semiconductor waferare provided on the mounting surface of the stage. In this stage also,at least some of the voltage applying electrode and the voltagemeasuring electrodes are formed in the form of a belt. These electrodesare disposed alternately on the mounting surface of the stage. Such aconfiguration prevents a difference from occurring in a measuring resultdue to a difference in position of the semiconductor wafer in which aplurality of semiconductor chips have been formed.

Patent document 2 (Jpn. Pat. Appln. KOKAI Publication No. 2-166746,claim and page 2, upper right column, line 17 to page 3, upper leftcolumn, line 3) discloses the same kind of a stage as that disclosed inpatent document 1. The mounting surface of the stage is divided into 2N(N is an integer of 2 or more), and voltage applying electrodes andvoltage measuring electrodes are formed alternately on each division.The stage can exert the same operation and effect as those of the patentdocument 1.

Patent document 3 (Jpn. Pat. Appln. KOKAI Publication No. 11-64385(claim and paragraphs [0006] to [0007]) discloses a technologyconcerning a probe. By this technology, connection pads of a device andprobes are Kelvin-connected. Two probes are disposed in the vicinity ofeach other such that each of them can be electrically connected to asingle connection pad. When the probes are pressed by the connection padso that both of them make contact with each other, the probes aredeformed elastically and make contact with the connection pads with tipsof the two probes approaching with a fine interval.

The inventions described in the patent documents 1 and 2 can reduce thebad influence of the internal resistance of the collector electrode upona measurement result when the collector electrodes formed on the rearface of a plurality of power devices and two kinds of electrodes formedon the mounting surface of the stage are electrically connected.However, no measure concerning connection of the probes and theelectrodes of the device is taken. Therefore, by pressing the probesagainst the electrodes in the same manner as in the prior art, an oxidefilm on the electrode is scraped away and the probes are brought intoelectrical contact with the electrodes. Thus, there is a fear that theprobes and electrodes may be damaged. If the size and the depth of aprobe trace are limited in order to avoid a failure in a bonding processin the case of a power device, contact between the probes and theelectrodes becomes unstable. Consequently, when a large current isapplied, sparking occurs, thereby possibly damaging the probes. A lossthat occurs in the electrical path between the probes and the electrodeinduces malfunction or the like, rendering accurate inspectionimpossible.

Although the probes described in patent document 3 can prevent theinfluence of foreign matter adhering to the probes, the probes arepressed against the connection pad conventionally, in order to bring theconnection pads and the probes into contact with each other. As aresult, the same problem as technology of patent document 1 exists.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is providedan inspection method for inspecting the electrical characteristics of aninspection object W′. The inspection method comprises:

(a) mounting the inspection object on a mounting surface of a stage,

the mounting surface of the stage comprising at least one third pair ofelectrodes,

the third pair of electrodes having a first electrode and a secondelectrode, the inspection object having a first surface and a secondsurface, the first surface comprising at least one conductive layer Q,the inspection object being mounted on the mounting surface such thatthe conductive layer is in contact with the third pair of electrodes;and

(b) applying a voltage to between at least one third pair of electrodeson the stage so as to generate a fritting phenomenon, and forming anelectrical path between the third pair of electrodes and the conductivelayer by using the fritting phenomenon.

The inspection method preferably comprises any one of the followingitems (1) to (4), or a combination of some of items (1) to (4):

(1) after the electrical path is formed between the third pair ofelectrodes and the conductive layer, connecting the third pair ofelectrodes to a test circuit 20;

(2) further comprising, before or after the step (b), or at the sametime:

(c) with at least one pair of probes kept in contact with at least onefourth electrode P on the second surface of the inspection object,applying a voltage between the pair of probes so as to generate afritting phenomenon, and forming an electrical path between each probeof the pair of probes and the fourth electrode by using the frittingphenomenon;

(3) after the electrical path is formed between each of the pair ofprobes and the fourth electrode, connecting at least one probe of thepair of probes to a test circuit; and

(4) the device is a power device.

According to a second aspect of the present invention, there is providedan inspection apparatus for inspecting the electrical characteristics ofan inspection object W′. The inspection apparatus comprises: a stage onwhich at least one inspection object W′ is mounted (the stage comprisesa mounting surface 11C which mounts the inspection object, and themounting surface comprises at least one third pair of electrodes); aprobe card 12 disposed above the stage and having a plurality of probes;a first fritting power supply which applies a fritting voltage betweenat least one pair of probes which makes contact with an electrode on asecond surface of the inspection object and the electrode; and a secondfritting power supply which applies a fritting voltage between a thirdpair of electrodes on a first surface of the inspection object and aconductive layer of the stage.

Preferably, the inspection apparatus further comprises:

(5) the inspection object having a first surface and a second surface,the first surface comprising at least one conductive layer Q, the secondsurface comprising at least one fourth electrode P, the inspectionobject being mounted on the mounting surface such that the conductivelayer is in contact with the third pair of electrodes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1A is a side view showing major portions of en embodiment of aninspection apparatus of the invention.

FIG. 1B is a schematic diagram showing a connection relation among apair of probes, a fritting. power supply and a test circuit.

FIG. 2 is a schematic diagram for explaining a fritting phenomenonbetween the pair of probes of the inspection apparatus and an electrodeof a device shown in FIGS. 1A and 1B.

FIG. 3 is a circuit diagram showing another fritting circuit for use inthe inspection apparatus shown in FIGS. 1A and 1B.

FIG. 4A is a plan view showing a relation between a stage of theinspection apparatus shown in FIG. 1 and a device.

FIG. 4B is a sectional view showing the relation between the stage ofthe inspection apparatus and the device shown in FIGS. 1A and 1B.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention can solve at least one of theabove-described problems. The embodiment of the invention may beconfigured so as to form a stable electrical path between probes anddevices without damaging or consuming the probes. The embodiment of theinvention may be configured so that electrical connection is carried outsecurely and stable inspection is executed without any malfunctionsecurely.

Hereinafter, the invention will be described on the basis of theembodiment shown in FIGS. 1 to 4. An inspection apparatus 10 of theembodiment comprises, as shown in FIG. 1A, a stage 11 (preferably, thisstage can be moved horizontally and vertically) for mounting aninspection object (for example, a device or plural devices formed on asubstrate W such as a wafer) and a probe card 12 disposed above thestage 11 and having a plurality of probes 13 (hereinafter, the substrateand inspection object are referred to as “wafer” and “device”,respectively). As shown in FIGS. 1A and 1B, in a state in which theplurality of probes 13 on the probe card 12 are kept in contact with afourth electrode P formed on a second surface 32 of the device W′, ameasurement signal is transmitted to the device from a test circuit 16through the probe 13, so that the electrical characteristics of thedevice are inspected. The diameter of the tip of each of the probes 13may be about 20 μm, and the probes 13 may be formed of conductive metalsuch as tungsten. The probe card 12 may be of such a type that theprobes are brought into contact with a plurality of devices on a wafercollectively. If a probe card which makes such collective contact isused, a plurality of devices can be inspected with a single contact.

The probes 13 are preferred to have a configuration in which a firstprobe 13A for applying a fritting voltage and a second probe 13B fordetecting a current of the fritting voltage make a pair as shown in FIG.1B. Plural pairs of probes 13 each comprising the first and secondprobes 13A, 13B make contact with a single electrode (hereinafter a pairof first and second probes 13A, 13B is called “pair of probes 13”). Asshown in FIG. 1B, each of the pair of probes 13 may be connected to afritting power supply 15 or the test circuit 16 by switching a relayswitch 14.

When the pair of probes 13 is connected to the first fritting powersupply 15 through the relay switch 14, a voltage is applied from thefirst fritting power supply 15 to between the first probe 13A and thesecond probe 13B of the pair of probes 13 as schematically indicated inFIG. 2. This voltage generates a fritting phenomenon, so that aninsulation film such as an oxide film on the fourth electrode (forexample, made of aluminum) P is broken, and the first and second probes13A, 13B make electrical contact with the fourth electrode so as to forman electrical path between the both. By using the fritting phenomenon,the pair of probes 13 can be brought into electrical contact with theelectrode with a small pressure (for example, 0.1 to 1.0 g/probe) evenif the oxide film exists on the electrode. As a consequence, apossibility that the electrode or the probe may be mechanically damagedis low, so that the electrical path can be formed securely.

The fritting phenomenon mentioned here refers to a phenomenon in which,when with a voltage applied to an insulation film such as an oxide filmformed on the surface of metal (electrode in the invention), potentialgradient turns to about 10⁵ to 10⁶ V/cm, a current flows, and theinsulation film is destroyed.

To form a plurality of electrical paths in one electrode of the powerdevice, it is permissible to build a semiconductor driver 14A or thelike into a fritting circuit and apply a voltage to the plural pairs ofprobes 13 at the same time to generate the fritting phenomenon. In thiscase, the relay switch may be omitted.

A diode 15B is used in the fritting circuit shown in FIG. 3. The diode15B may be disposed in an opposite orientation to FIG. 3, and may beomitted depending on a case.

In FIG. 2, plural pairs (two pairs in FIG. 2) of probes 13 make contactwith one fourth electrode P. The value of contact resistance betweeneach of the first and second probes 13A, 13B and the fourth electrode Pcan be of different values R1 to R4 because of diffusion or the like ofthe thickness of the oxide film on the fourth electrode P. Because thecontact resistances R1 to R4 are connected in parallel, the entirecontact resistance decreases as the number of the pairs of probes 13increases.

Due to the fritting phenomenon, electrical paths are formed between eachof the first and second probes 13A, 13B, and the fourth electrode P, sothat the first and second probes 13A, 13B can be stably connected to thefourth electrode P. With this condition, as shown in FIG. 1B, the relayswitch 14 is changed from the fritting power supply 15 to the testcircuit 16 and connected. That is, the first probe 13A is connected to amonitor signal line of the test circuit 16, and the second probe 13B isconnected to an inspection signal line of the test circuit 16. The testcircuit 16 can inspect the electrical characteristics of a devicesecurely and accurately.

Because electrical paths are formed between each of the first and secondprobes 13A, 13B of each pair of probes 13, and the fourth electrode P,plural pairs of probes 13 form a collective electrical path even if avoltage applied to the first and second probes 13A, 13B is low. Aninspection of a power device to which a large current and voltage areapplied, such as a dynamic test and switching test can be carried out byusing the probe card 12. The number of the pairs of probes 13 can be setdepending on the magnitude of current or voltage.

FIGS. 4A and 4B show the stage 11 of the inspection apparatus 10 whichcan be used for an inspection of the power device. As shown in FIGS. 4Aand 4B, a plurality of third pairs of electrodes 17 are formed on themounting surface 11C of the stage 11. In FIGS. 4A and 4B, a plurality ofthird pairs of electrodes 17 (for example, 16 pairs) each are formed ofa first electrode 17A and second electrode 17B. Each third pair ofelectrodes 17 includes the first electrode 17A and second electrode 17Blike the pair of probes 13. The third pair of electrodes 17 is switchedbetween a second fritting power supply 19 and a test circuit 20 througha relay switch 18 (FIG. 4B) and connected thereto. The second frittingpower supply 19 may be used together with the first fritting powersupply 15 (FIG. 1).

When the third pair of electrodes 17 is connected to the fritting powersupply 19, a fritting phenomenon is generated by a voltage from thefritting power supply 19. The first and second electrodes 17A, 17B ofthe third pair of electrodes 17 make electrical contact with aconductive layer (collector electrode) Q formed on the first surface 31of the wafer W or device W′ (for example, a power device) so as to forman electrical path, thereby achieving electric connection. The first andsecond electrodes 17A, 17B of the third pair of electrodes 17 aredisposed entirely in a matrix such that they adjoin each other as shownin FIGS. 4A. The third pairs of electrodes 17 may be disposed on theentire rear face of the wafer W. By generating a plurality of thirdpairs of electrodes 17 in the conductive layer Q, the third pairs ofelectrodes 17 may be electrically connected to a common electrode formedon the rear face of the wafer W or device W′ by reducing a deviationdepending on a place. As a result, an inspection with little error canbe carried out.

If the third pair of electrodes 17 is switched from the second frittingpower supply 19 to the test circuit 20 by the relay switch 18 in a statein which electrical connection is maintained, the third pair ofelectrodes 17 is connected to the test circuit 20 from the frittingpower supply 19. For example, the first electrode 17A is connected tothe monitor signal line and at the same time, the second electrode 17Bis connected to the inspection signal line. With the third pair ofelectrodes 17 electrically connected to the conductive layer Q of thedevice securely and stably, the test circuit 20 can inspect theelectrical characteristics of the device securely and accurately.

The stage 11 can be formed of ceramic such as aluminum nitride. A copperplating layer 11A is formed on the mounting surface 11C as shown in FIG.4B. A plural pairs of electrodes 17 are formed on the copper platinglayer 11A. Preferably, an insulation film (for example, a polyimideresin film) 11B is overlaid on the copper plating layer 11A between thefirst and second electrodes 17A, 17B. The insulation film 11Belectrically insulates between the adjoining electrodes 17A and 17B.Preferably, for example, a step of about 1 μm is formed between thesurface of the third pair of electrodes 17 and the surface of thepolyimide resin film 11B. The wafer W or device W′ makes contact withonly the third pair of electrodes 17.

Pads 21, which are connected to the first and second electrodes 17A,17B, are disposed on the outer peripheral portion of the mountingsurface 11C. These pads 21 may be disposed so as to surround theplurality of third pairs of electrodes 17. The pads 21 are overlaid onthe copper plating layer 11A in the same manner as in the first andsecond electrodes 17A, 17B, and preferably, the respective pads 21 areelectrically insulated from one another by the polyimide resin film 11B.The electrodes 17A, 17B of the third pair of electrodes 17 are connectedto the relay switch 18 through the pads 21.

As shown in FIG. 4B, discharge air passages 22 which are open in thesurface of the first and second electrodes 17A, 17B are preferablyformed in the stage 11. These discharge air passages 22 go through fromthe surfaces of the first and second electrodes 17A, 17B to the rearface of the stage 11. A vacuum jacket 23 is mounted on the rear face ofthe stage 11, and a vacuum air discharge unit 22A is connected to thevacuum jacket. 23. The vacuum air discharge unit 22A discharges air fromwithin the vacuum jacket in the direction of an arrow so as to attractthe wafer W or device W′ onto the pairs of electrodes 17 with vacuum.

An example of an inspection method using the inspection apparatus ofthis embodiment will be described. In FIG. 4B, the device (for example,a power device) is mounted on the stage 11. In this case, the conductivelayer Q provided on the first surface 31 of the device makes contactwith the plurality of third pairs of electrodes 17 provided on themounting surface 11C of the stage. By attracting onto the pairs ofelectrodes 17 with the vacuum air discharge unit, the wafer W is fixedon the stage 11.

The stage 11 moves to just below the probe card 12.

The stage 11 rises, and the fourth electrode P on the second surface 32of the device W′ comes into contact with the pairs of probes 13 of theprobe card 12. By. overdriving the stage 11 about 50 μm, the pairs ofprobes 13 make contact with the fourth electrodes 4 of the device W (W′)with stylus pressure of about 1 g/piece (FIGS. 1A and 2).

The relay switch 18 connects the third pairs of electrodes 17 with thesecond fritting power supply 19. A voltage is applied from the secondfritting power supply 19 to the third pairs of electrodes 17. Thefritting phenomenon occurs, so that electrical paths are formed betweeneach of the electrodes 17A, 17B of each of the plurality of third pairsof electrodes 17, and the conductive layer Q on the first surface of thedevice.

The relay switch 14 connects the first fritting power supply 15 to thepairs of probes 13 on the side of the probe card 12. A voltage isapplied form the first fritting power supply 15 to the pairs of probes13. The fritting phenomenon occurs, so that electrical paths are formedbetween each of the probes 13A, 13B of each of the plural pairs ofprobes 13 and the fourth electrodes P of the device. The third pairs ofelectrodes 17 on the stage 11 and the conductive layer Q on the firstsurface 31 of the device W′ are electrically connected stably throughthe electrical paths.

The relay switch 18 changes the plurality of third pairs of electrodes17 from the second fritting power supply 19 to the test circuit 20 onthe stage 11 side. The relay switch 14 changes the plurality of pairs ofprobes 13 from the first fritting power supply 15 to the test circuit 16on the probe card 12 side. With a voltage or a large current applied tothe plurality of probes 13, the electrical characteristics of the devicecan be inspected by using the test circuits 16, 20.

According to this embodiment, as described above, it is preferable thatthe wafer W or device W′ is mounted on the stage 11 and that the pairsof probes 13 are brought into contact with the fourth electrodes P. Thefritting phenomenon is generated by applying a fritting voltage to eachof the pairs of probes 13. Using the fritting phenomenon, electricalpaths are formed between each of the probes 13A, 13B of the pairs ofprobes 13 and the fourth electrode P. As a result, the pair of probes 13and the fourth electrode P may be electrically connected to each othersecurely with an extremely low stylus pressure. A stable electrical pathmay be formed between the fourth electrode P of the device and each ofthe probes 13A, 13B without damaging or consuming the first and secondprobes 13A, 13B of the pair of probes 13 so as to form a secure electricconnection. Even if a large current is applied to the device from thepair of probes 13, the electrical characteristics can be inspectedsecurely and stably without any malfunction.

Preferably, on the stage 11 side, in a state in which the plurality ofthird pairs of electrodes 17 formed on the mounting surface 11C and theconductive layer (collector electrode) formed on the first surface 31 ofthe wafer W or the device are kept in contact with each other, thefritting voltage is applied to the plurality of third pairs ofelectrodes 17 so as to generate the fritting phenomenon. The electricalpath is formed between each of the respective electrodes 17A, 17B of thethird pair of electrodes 17 and the conductive layer Q by using thisfritting phenomenon. Therefore, stable electric connection can be formedbetween the third pair of electrodes 17 on the stage 11 and theconductive layer Q on the first surface 31 of the device W′.

According to this embodiment, it is preferable that, after electricalpaths are formed between each of the plurality of pairs of probes 13 andthe fourth electrode P of the device, the pair of probes 13 is connectedto the test circuit so as to form the electrical path between each ofthe plurality of third pairs of electrodes 17 and the conductive layer(collector electrode) on the second surface of the device, and then eachof the pairs of electrodes 17 is connected to the test circuit 20. Thetest circuits 16, 20 can inspect the electrical characteristics of thedevice securely.

According to this embodiment, the air discharge passages, which are opento the top face of each of the electrodes 17A, 17B on the mountingsurface 11C of the stage 11, are provided in the stage 11. The wafer Wcan be fixed securely on each of the electrodes 17A, 17B, so that therespective electrodes 17A, 17B and the conductive layer Q on the firstsurface 31 of the device can be connected electrically, simply andeasily.

Preferably, the pads 21 electrically connected to the respectiveelectrodes 17A, 17B of the third pair of electrodes 17 are provided onthe outer peripheral portion of the mounting surface 11C of the stage11. The respective pairs of electrodes 17 may be connected to the relayswitch easily through the pads 21.

The present invention is not restricted to the above-describedrespective embodiments, and any inspection method and inspectionapparatus for electrically connecting the probes and the electrodes ofdevice or the third pair of electrodes formed on the mounting surface11C of the stage and the conductive layer Q of the first surface of thedevice by using the fritting phenomenon are included in the presentinvention.

According to the invention, a case of inspection of the power device hasbeen described, and the present invention can be applied widely to otherdevices.

According to the present invention, electric connection can be performedsecurely by forming a stable electrical path between the probe and thedevice without damaging or consuming the probe. As a consequence, theinvention can provide an inspection method and inspection apparatuscapable of carrying out a stable inspection without any malfunction.

1. An inspection method for inspecting the electrical characteristics ofan inspection object, the inspection method comprising: (a) mounting theinspection object on a mounting surface of a stage, the mounting surfaceof the stage comprising at least one third pair of electrodes, the thirdpair of electrodes having a first electrode and a second electrode, theinspection object having a first surface and a second surface, the firstsurface comprising at least one conductive layer, the inspection objectbeing mounted on the mounting surface such that the conductive layer isin contact with the third pair of electrodes; and (b) applying a voltageto between at least one third pair of electrodes on the stage so as togenerate a fritting phenomenon, and forming an electrical path betweenthe third pair of electrodes and the conductive layer by using thefritting phenomenon.
 2. The inspection method according to claim 1,further comprising: after the electrical path is formed between thethird pair of electrodes and the conductive layer, connecting the thirdpair of electrodes to a test circuit.
 3. An inspection method accordingto claim 1, further comprising, before or after the step (b), or at thesame time: (c) with at least one pair of probes kept in contact with atleast one fourth electrode on the second surface of the inspectionobject, applying a voltage to between the pair of probes so as togenerate a fritting phenomenon, and forming an electrical path betweeneach probe of the pair of probes and the fourth electrode by using thefritting phenomenon.
 4. The inspection method according to claim 3,further comprising: after the electrical path is formed between each ofthe pair of probes and the fourth electrode, connecting at least oneprobe of the pair of probes to a test circuit.
 5. The inspection methodaccording to claim 1, wherein the device is a power-system device.
 6. Aninspection apparatus for inspecting electrical characteristics of aninspection object, comprising: a stage on which at least one inspectionobject is mounted, the stage comprising a mounting surface which mountsthe inspection object, the mounting surface comprising at least onethird pair of electrodes; a probe card disposed above the stage andhaving a plurality of probes; a first fritting power supply whichapplies a fritting voltage to between at least one pair of probes whichmakes contact with an electrode on a second surface of the inspectionobject and the electrode; and a second fritting power supply whichapplies a fritting voltage to between a third pair of electrodes on afirst surface of the inspection object and a conductive layer of thestage.
 7. An inspection method for, with an inspection object placed ona stage and a plurality of pairs of probes formed on the inspectionobject kept in contact with electrodes of a plurality of devices,inspecting each of the devices, comprising a step of applying a voltageto said plurality of pairs of probes in contact with the electrodes ofthe devices independently or at the same time, and forming an electricalpath between each probe of the pairs of probes and the electrode byusing a fritting phenomenon.